import math

def twiddle_tile(srcfile, destfile, twiddlefunc):
    for line in srcfile:
        gps = line.split()
        if len(gps) == 4 and gps[0] == "v":
            vert = [float(v) for v in gps[1:]]
            if vert[1] < 0.0: # don't twiddle bottom of tile
                dest.write(line + "\n")
            else:
                vert_prime = twiddlefunc(vert[0], vert[1], vert[2])
                dest.write("v {} {} {}\n".format(*vert_prime))
        else: # line is not a vertex, so write it back unchanged
            dest.write(line + "\n")

def points(x, y, z):
    theta = math.atan2(z, x)
    amp = math.sin(theta * 25) * 1.5
    return (x, y+amp, z)

if __name__ == '__main__':
    srcfn = "tile_blank.obj"
    destfn = "tile_transform.obj"
    with open(srcfn, "rt") as src:
        with open(destfn, "wt") as dest:
            twiddle_tile(src, dest, points)